After flashing various firmwares and hacking almost every phone I've ever owned, I feel like an absolute noob asking this question.... but I'm selling my AT&T 8100 to a T-Mobile user and need to unlock it. Is it as simple as calling AT&T, since I own the phone and have since upgraded to a Tilt?

Feel free to flame me... but I did a cursory search and was flooded by posts of people asking for unlock codes.